Chicken eggs are one of the most important foods in the human diet, and are an exceptional source of proteins and fats, as well as amino acids and fatty acids. Every year in the United States an estimated 90 billion eggs are produced, with three fourths of these eggs being used for human consumption. An estimated 250 eggs per person are consumed annually in the United States.
Many of the eggs consumed by humans are eaten as food ingredients, rather than directly as cooked eggs (such as boiled, fried, poached, etc.). In some cases whole eggs are used as food ingredients, for example as baking applications. However, it is often desirable to use just a portion of an egg as a food ingredient. For example, egg yolk is an excellent emulsifier and surfactant, and is an essential component of mayonnaise and various other foods. The egg yolk makes up approximately one third of the liquid weight of an egg, and is high in fats and fatty acids. Important fat soluble vitamins (A, D, E, and K) are found in egg yolk, as are unsaturated fatty acids (e.g. oleic acid, linoleic acid, palmitoleic acid, and linolenic acid) and saturated fatty acids (e.g. palmitic acid, stearic acid, and myristic acid). Egg yolks also contain some proteins, typically on the order of 2 to 3 grams out of about 15 to 20 grams of yolk within an egg weighing approximately 50 grams.
The egg white, known as well as the albumen, also has unique uses as a result of having high protein content. Egg whites are used in many products, such as to make mousse and to enhance protein content of foods. Egg white is approximately two-thirds of the total weight of an egg, with approximately 90 percent of that weight coming from water. The remaining weight of the egg white comes primarily from protein, along with various trace minerals, vitamins, some fats, and glucose. A typical large egg may contain 35 to 40 grams of egg white, of which about 4 to 5 grams are proteins. The most common protein in egg whites is ovalbumen, which accounts for over half of the proteins. Ovotransferrin and ovomucoid are additional primary proteins, with other proteins including ovoglobulin G2, Ovoglobulin G3, ovomucin, lysozyme, ovoinhibitor, ovoglycoprotein, flavoprotein, ovomacroglbulin, avidin, and crystatin. The egg white contains no dietary cholesterol, but does contain small quantities of other lipids and fats.
Thus, egg yolks are very high in fats, but low in proteins; while egg whites are very high in proteins, but low in fats. However, egg yolks do contain some proteins, and egg whites do contain small quantities of fats.
Due to their different compositions and uses, it is often desirable to separate egg yolks and egg whites from one another. Various systems and methods have been developed for separation of eggs into yolks and whites. Separation of yolk and white from whole eggs can be done at high speeds under automated conditions, and can very effectively separate the yolks and eggs, with relatively little mixing of the yolk and eggs.
Despite the uses of existing technology to separate yolks from whites, a need exists for further separation of egg components, including components in both the egg yolk and the egg white. This is true because the mere physical separation of the egg yolk from the egg white is not always sufficient to maximize use of the yolks and whites. For example, with regard to the yolk, it is desirable to also remove the yolk proteins from the yolk fats for at least two reasons: First, traditional uses of the yolk as an emulsifier improve upon reduction of the protein content. Second, the removal of the protein provides an isolated protein material that has further uses for applications where high-protein materials are desired and where the specific yolk proteins are desired in isolated form. Similarly, with regard to the egg white, removal of non-protein materials creates a higher quality isolated protein. Also, separation of the proteins into different sizes and types can have significant benefits for production of specialized products.
In addition to the benefits associated with separating proteins and fats from nearly pure egg yolks and pure egg whites, a need also exists for separation of proteins and fats from mixtures that contain both egg yolks and egg whites. Such mixtures are created, for example, as a result of incidental breakage of yolks during the separation of the yolk from the white during the cracking process. Similarly, some egg white can remain with the egg yolk during cracking. These mixtures result in increased levels of proteins in the separated egg yolk, and increased levels of fats in the separated egg whites. The ability to separate the primary constituents (proteins and fats) within the mixtures can have meaningful advantages in terms of nutritional value and performance for specific applications (such as to create mayonnaise).
Yet another scenario for separation of fats and proteins in eggs arises due to production of eggs at hatcheries (or other facilities) where the eggs are not primarily raised for human consumption. For example, sterile eggs and non-incubated eggs from hatcheries are not produced or used for human consumption. Although these hatchery-derived eggs are typically not provided for regular human consumption, they are still of value as a source of fats and proteins. Currently the hatchery-derived eggs are not processed so as to be separated into yolk and white components, because they are produced in facilities that are not served by a high speed cracker and separator. Instead, the hatchery-derived eggs are often broken and run through a separator to remove the egg shells, a process that mixes the egg yolks and proteins. This mixed egg yolk and white, which is considered inedible for human consumption, is typically used as a combined additive for uses such as animal feed. However, a need exists for a means to effectively separate the fats and proteins from these mixtures of inedible eggs so as to gain the maximum benefit of the proteins and fats, which is best achieved by separating them from one another
As noted above, the most prevalent means of separating egg components is limited to the separation of whole yolks and whites from one another. This separation is commonly performed at high speeds and efficiencies using automatic equipment. However, alternative efforts for further separation of egg components into more isolated components (such as proteins and lipids) have been attempted. Unfortunately, these methods have proven problematic for various reasons, including because the processes are inefficient, impractical, or have other deficiencies.
An example of such efforts is found in U.S. patent application Ser. No. 11/971,802 (“the '802 application”), assigned to Biova, Inc., and which is directed to a method of separating lipids from an egg mixture by using a cross-linking reagent. The cross-linking reagent is added to an egg mixture containing lipids and solubilized proteins, causing the lipids to crosslink so they can be separated from the proteins. Suitable crosslinking reagents include cyclobetadextran, silicon dioxide, colloidal silica material, fumed silica materials, and synthetic calcium silicate hydrates. The method of the '802 application can include adjusting the pH level of the egg mixture to a pH at which the cross-linking reagent is functional so that cross-linking of the lipids occurs. The proteins are subsequently separated from the cross-linked lipids to provide a separated protein. The separated proteins may be obtained by subjecting the egg mixture to one or membranes or filters of various sizes to separate or further isolate proteins or populations of proteins of interest.
Although it may be possible to separate proteins and fats derived from eggs using the teachings of the '802 application, significant drawbacks are associated with the methods and materials it discloses. First, the inclusion of the cross-linking reagent is problematic if the egg components will eventually be consumed by humans, in that there is often opposition on the part of the public and regulatory agencies to consume materials that have been subject to adulteration by organic reagents, such as cyclobetadextran, or by inorganic materials such as colloidal or fumed silica materials. The aversion to the use of these cross-linking reagents exists, in part, because of the potential for undesirable modification or contamination of the crosslinked ingredients. Although naturally occurring silica is widespread in nature, its use in food processing is unusual, and risks opposition by consumers even if little or none of the crosslinking agent remains in the separated components.
Second, the use of the crosslinking reagent necessarily adds expense to the processing of the egg mixture, both because of the cost of the crosslinking reagent itself, as well as the costs associated with the additional steps of crosslinking the fats and subsequent removal of the crosslinking agent (such as silica) from the fats after separation of the fats and proteins, assuming the fats are intended for further use. Thus, not only does the use of a reagent result in potentially problematic alteration and/or contamination of the egg material with crosslinker, especially the egg yolk (since it is the fats that are crosslinked, and fats are primarily found in the yolk), but the use of the reagent adds expense and complexity to the egg processing methods: A step must be made to add the reagent to the egg mixture, one to induce crosslinking of the fats, as well as steps to reverse the crosslinking, when possible, after separation of the crosslinked egg fats and egg proteins. These steps all take time, equipment, and effort.
Yet another problem with the methods taught in the '802 application is that the use of the reagents creates an issue with regard to waste silica (or other crosslinking agent), which must be removed from the fats for most uses of the fats, and which can result in creation of an undesirable waste stream that must be disposed of, even if it is not hazardous. Today there is an increased emphasis on processes that use limited resources and which produce little or no waste product, and the '802 application does not fully satisfy this objective.
Therefore, a need exists for methods and equipment for separating egg components into proteins and fats (or other substituents, such as amino acids). Such methods and equipment should include the ability to separate the components of exclusively egg yolk materials, exclusively egg white materials, and mixtures of various levels of egg yolk and egg white. Preferably such methods and equipment can be efficient, cost effective, produced without undesirable alteration of the egg components (such as alteration with cross linkers), and do not create excessive undesirable waste streams.